This invention relates to reducing atmospheric pollution during the combustion of diesel and other hydrocarbon fuels. The invention further relates to organic additives useful for reducing carbon monoxide, soot, smoke, and particulate emissions formed during the combustion of hydrocarbon fuels.
When fuel and air are mixed and ignited in the combustion chamber of an internal combustion engine, most of the fuel is burned to produce carbon dioxide and water which is discharged into the air with the engine exhaust gases. However, because the fuel and air are present in the combustion chamber for a finite period and the fuel and air have only a finite length of time to react at the temperatures and pressures present within the engine's combustion chamber, some of the fuel does not burn, is only partially burned, or reacts by itself without interacting with oxygen. The result of this time limitation is that other products, namely, carbon monoxide, hydrocarbons, and solid carbonaceous particulate matter, form during fuel combustion, and these are also discharged into the air.
The particulate matter formed during the combustion of hydrocarbon fuels, especially middle distillate fuels, such as diesel fuels, and residual fuels, such as non-distillate fuel oils, is commonly referred to as soot. When present in sufficient particle size and quantity, soot in engine, boiler or burner exhaust gases appears as a dense black plume. This is highly undesirable since it results in environmental pollution, engine design limitations, and possible health problems.
Diesel-type engines are well known for being highly durable and fuel efficient. Because of this durability and fuel efficiency, diesel-type engines have long been used in heavy-duty motor vehicles, such as trucks, buses, locomotives, and marine engines. Recently, however, concern over the contribution of diesel solid particulate emissions to decreasing atmospheric visibility in urban areas and potential health hazards has led to the United States Environmental Protection Agency promulgating a set of exhaust emission standards for heavy-duty diesel engines at 40 CFR 86, subpart A. In regard to combustion particulates, these state that for the 1988 model year, the maximum allowable level of solid particulates emitted is 0.6 grams per brake-horsepower-hour. For the 1991 model year, this level drops to 0.25 grams for trucks and 0.10 grams for buses, and, for the 1994 model year, the level is set at 0.10 grams for all such vehicles. These standards present scientists with more difficult challenges in the areas of diesel engine component and combustion system design and advanced fuel technology.
One approach reportedly being considered for helping to meet these goals is that of reducing the aromatic content of diesel fuel, now typically in the range of 30 to 35 volume percent, to below about 20 volume percent, and the sulfur content to below about 0.05 weight percent. It is estimated that making such changes in diesel fuel would cost at least 15 to 20 cents per gallon at the refinery level. Price increases at the consumer level would be expected to be somewhat higher.
Another approach is described by Nichols, Jr. in U.S. Pat. No. 4,240,802, wherein the addition of a minor amount of a cyclopentadienyl manganese tricarbonyl and a lower alkyl or cycloalkyl nitrate to a hydrocarbon fuel is disclosed. These compounds are described as useful in reducing carbonaceous particulate emissions from fuel oil. However, the manganese content in such an additive creates problems with MnO.sub.x emissions in that they are toxic, and the overall weight of solid particulate matter removed from the exhaust is relatively unchanged.